1. Field of the Invention
This invention relates to ladders and more particularly to levellers on the bottoms of the side rails thereof for use on sloped or uneven surfaces.
2. Description of Related Art
Ladders frequently must be used on sloped or irregular surfaces. For example, ladders used on the exteriors of buildings often encounter sloped ground. On the insides of buildings, stairs present difficulties for ordinary ladders. In both circumstances the bottoms of the side rails may not contact the ground or floor simultaneously if the ladder is completely vertical. If the ladder is sloped to conform to the ground or floor, then it is likely to be unsafe.
Accordingly, several different types of apparatuses have been developed in the past in order to level the legs of a ladder so that they simultaneously contact uneven surfaces while the ladder is perfectly vertical. That is particularly important for long extension ladders where even a slight deviation from the vertical may cause the ladder to slip in use.
For example, U.S. Pat. No. 5,174,412 to Vega shows a ladder leveller which includes a member which engages the rungs of the ladder. There is a slidable leg mounted on the member and a plurality of matching apertures in the member and leg. A pin selectively locks the leg with respect to the member so that the leg extends a required amount below the ladder in order to level it.
U.S. Pat. No. 5,107,958 to Johnson shows a ladder leveller including a pair of sleeves which fit over the bottoms of the side rails. Threaded screw bolts are used to lock the sleeves in position so that they project a required amount below the side rails in order to level the ladder.
U.S. Pat. No. 5,154,257 to Mirles shows a ladder with a telescopically extending extension at the bottom each leg. These can be locked in a desired position to level the ladder by means of a number of different types of locking mechanisms.
While some of these prior art devices function satisfactorily, they typically suffer one or more drawbacks which limit their potential market and widespread acceptance. For example, many of these devices are relatively complicated and include many different components which must be assembled together. In other cases, installing the apparatus on a ladder may be difficult for the average person. Some of the apparatuses are heavy or make the ladder awkward to use.